Protein-deamidating enzyme, gene encoding the same, production process therefor, and use thereof

ABSTRACT

A novel enzyme which has an activity to release side chain carboxyl groups and ammonia from a protein by acting upon side chain amido groups in the protein. This invention relates to a method for the production of an enzyme, which comprises culturing in a medium a strain that belongs to a bacterium classified into  Cytophagales  or  Actinomycetes  and has the ability to produce an enzyme having a property to deamidate amido groups in protein, thereby effecting production of said enzyme, and subsequently collecting said enzyme from the culture mixture. It also relates to a method for the modification of protein making use of a novel enzyme which directly acts upon amido groups in protein as well as to an enzyme which has a property to deamidate amido groups in protein and a gene which encodes said enzyme.

This application is a Divisional Application of the prior applicationNo. 09/793,495 (U.S. Pat. No. 6,770,469) filed Feb. 27, 2000, which is aDivisional Application of the prior application No. 09/324,910 (U.S.Pat. No. 6,251,651) filed Jun. 3, 1999.

FIELD OF THE INVENTION

This invention relates to a novel enzyme, namely a novel enzyme whichacts upon side chain amido groups in protein and thereby releases sidechain carboxyl groups and ammonia, and to a production method thereof.More particularly, it relates to a method for the production of anenzyme having a property to deamidate amido groups in protein, whichcomprises culturing a bacterial strain capable of producing an enzymehaving a property to deamidate amido groups in protein, that belongs toCytophagales or Actinomycetes, more particularly to the genusChryseobacterium, Flavobacterium, Empedobacter, Sphingobacterium,Aureobacterium or Myroides, in a medium, thereby allowing the strain toproduce said enzyme, and subsequently collecting said enzyme from theculture mixture. This invention also relates to a method for themodification of protein, which uses a novel enzyme having a property todirectly act upon amido groups in protein. It also relates to an enzymewhich has a property to deamidate amido groups in protein, to a genewhich encodes said enzyme, to a vector which contains said gene, to atransformant transformed with said vector, and to a method for theproduction of an enzyme having a property to deamidate amido groups inprotein, which comprises culturing said transformant in a medium,thereby allowing the transformant to produce said enzyme, andsubsequently collecting said enzyme from the culture mixture.

BACKGROUND ART

Glutaminase/asparaginase are enzymes which hydrolyzeglutamine/asparagine to convert them into glutamic acid/aspartic acidand ammonia, and it is well known that these enzymes are obtained fromanimals, plants and microorganisms. However, these enzymes specificallyact on free glutamine/asparagine and cannot deamidateglutamine/asparagine in peptides or polypeptides.

Also, transglutaminase is known as an enzyme which acts upon amidogroups existing in a peptide state. Transglutaminase catalizes thereaction of introducing an amine compound into protein by covalentbonding or the reaction of cross-linking the glutamine residue and lysinresidue of protein via ε-(γ-glutamyl)lysine-isopeptide bonding, in whichthe amido group of peptide bonded glutamine as an acyl donor and theamino group of the primary amine as an acyl acceptor. It is known that,when amine or lysin does not exits in the reaction system or blocked,water acts as an acyl acceptor and the glutamine residue in paptide isdeamidated to become glutamic acid residue. As described above,transglutaminase is basically an acyl group transferase. Accordingly,when allowed to act on a usual protein, this enzyme causes cross-linkingof protein and does not deamidate the protein. Accordingly,transglutaminase is different from the enzyme of the present invention.

In addition, Peptideglutaminase I and Peptideglutaminae II produced byBacillus circulans are known as an enzyme which performs deamidation byacting upon glutamine bonded in peptide. It is known that the formeracts on the glutamine residue existing at the C terminal of peptide andthe latter acts on the glutamine residue existing in the peptide.However, these enzymes hardly acts upon a high molecular weight proteinand acts only upon a low molecular weight peptide [M. Kikuchi, H.Hayashida, E. Nakano and K. Sakaguchi, Biochemistry, vol. 10, 1222-1229(1971)].

Also, plural studies have been made to attempt to allow these enzyme(Peptideglutaminase I and II) to act upon a high molecular weightprotein rather than a low molecular weight peptide. As a result, it hasbeen revealed that these enzymes do not substantially act on a highmolecular weight protein but act only on a protein hydrolysate peptide.Gill et al. reported that each of Peptideglutaminase I and II does notact on milk casein and whey protein both in native form and denaturedform. They also reported that, as a result of studies on activities onprotein hydrolysate, only Peptideglutaminase II acted only on peptidehaving a molecular weight of 5000 or less (B. P. Gill, A. J.O'Shaughnessey, P. Henderson and D. R. Headon, Ir. J. Food Sci.Technol., vol. 9, 33-41 (1985)). Similar studies were carried out byHamada et al. using soy bean protein and the result was consistent withthe result by Gill et al. That is, it was reported that these enzymesshowed deamidation percentage of 24.4% to 47.7% on soy bean peptide(Peptone), but did not substantially act on soy bean protein (0.4% to0.8%) (J. S. Hamada, F. F. Shih, A. W. Frank and W. E. Marshall, J. FoodScience, vol. 53, no. 2, 671-672 (1988)).

There is an report suggesting existence of an enzyme originating fromplant seed, which catalyzes deamidation of protein (cf. I. A. Vaintraub,L. V. Kotova, R. Shara, FEBS Letter, Vol. 302, 169-171 (1992)). Althoughthis report observed ammonia release from protein using a partiallypurified enzyme sample, it is clear that this report does not proveexistence of an enzyme of the present invention from the followingreasons. In this report, a partially purified enzyme sample was used,inexistence of protease activity was not confirmed, and no change inmolecular weight of substrate protein after the reaction was notconfirmed. Accordingly, this report does not exclude the possibilitythat plural enzymes (not one enzyme) such as protease, peptidase, etc.acted on protein to release glutamine/asparagine as free amino acids andammonia was released by glutaminase/asparaginase which deamidate thesefree amino acids. Similarly, there is a possibility thatglutamine-containing low molecular weight peptide produced in a similarway is deamidated by peptideglutaminase-like enzyme. In addition, thereis a possibility that deamidation occurred as a side-reaction byprotease. In particular, it should be noted that this report clearlydescribes that the partially purified preparation had glutaminaseactivity which acted on free glutamine to release ammonia.

Accordingly, there is no report until now which confirmed existence ofan enzyme which can catalyzes deamidation of on high molecular weightprotein by purification of the enzyme as a single protein and isolationand expression of the gene encoding the same.

In general, when carboxyl groups are formed by deamidation of glutamineand asparagine residues in protein, negative charge of the proteinincreases and, as the results, its isoelectric point decreases and itshydration ability increases. It also causes reduction of mutual reactionbetween protein molecules, namely, reduction of association ability, dueto the increment of electrostatic repulsion. Solubility and waterdispersibility of protein sharply increases by these changes. Also, theincrement of negative charge of protein results in the change of thehigher-order structure of the protein caused by loosening of itsfolding, thus exposing the hydrophobic region buried in the proteinmolecule to the molecular surface. In consequence, a deamidated proteinhas amphipathic property and becomes an ideal surface active agent, sothat emulsification ability, emulsification stability, foamability andfoam stability of the protein are sharply improved.

Thus, deamidation of a protein results in the improvement of its variousfunctional characteristics, so that the use of the protein increasessharply (for example, see Molecular Approaches to Improving Food Qualityand Safety, D. Chatnagar and T. E. Cleveland, eds., Van NostrandReinhold, New York, 1992, p. 37).

Accordingly, a large number of methods for the deamidation of proteinhave been studied and proposed. An example of chemical deamidation ofprotein is a method in which protein is treated with a mild acid or amild alkali under high temperature condition. In general, amido groupsof glutamine and asparagine residues in protein are hydrolyzed by anacid or a base. However, this reaction is non-specific and accompaniescutting of peptide bond under a strong acid or alkali condition. It alsoaccompanies denaturation of protein to spoil functionality of theprotein.

Accordingly, various means have been devised with the aim of limitingthese undesired reactions, and a mild acid treatment (for example, seeJ. W. Finley, J. Food Sci., 40, 1283, 1975; C. W. Wu, S. Nakai and W. D.Powie, J. Agric. Food Chem., 24, 504, 1976) and a mild alkali treatment(for example, see A. Dilollo, I. Alli, C. Biloarders and N. Barthakur,J. Agric. Food Chem., 41, 24, 1993) have been proposed. In addition, theuse of sodium dodecyl sulfate as an acid (F. F. Shih and A. Kalmar, J.Agric. Food Chem., 35, 672, 1987) or cation exchange resin as a catalyst(F. F. Shih, J. Food Sci., 52, 1529, 1987) and a high temperaturetreatment under a low moisture condition (J. Zhang, T. C. Lee and C. T.Ho, J. Agric. Food Chem., 41, 1840, 1993) have also been attempted.

However, all of these methods have a difficulty in completelyrestricting cutting of peptide bond. The cutting of peptide bond is notdesirable, because it inhibits functional improvement of proteinexpected by its deamidation and also causes generation of bitterness.Also, the alkali treatment method is efficient in comparison with theacid treatment method, but it has disadvantages in that it causesracemization of amino acids and formation of lysinoalanine which has apossibility of exerting toxicity.

On the other hand, some enzymatic deamidation methods have also beenattempted with the aim of resolving the aforementioned problems of thechemical methods. Namely, a protease treatment method under a high pH(pH 10) condition (A. Kato, A. Tanaka, N. Matsudomi and K. Kobayashi, J.Agric. Food Chem., 35, 224, 1987), a transglutaminase method (M. Motoki,K. Seguro, A. Nio and K. Takinami, Agric. Biol. Chem., 50, 3025, 1986)and a peptideglutaminase method (J. S. Hamada and W. E. Marshall, J.Food Sci., 54, 598, 1989) have been proposed, but each of these methodshas disadvantages.

Firstly, the protease method cannot avoid cutting of peptide bond as itsoriginal reaction. As described in the foregoing, cutting of peptidebond is nor desirable.

In the case of the transglutaminase method, it is necessary tochemically protect ε-amino group of lysine residue in advance, in orderto prevent cross-linking reaction caused by the formation of isopeptidebond between glutamine and lysine, as the original reaction of theenzyme. When a deamidated protein is used in food, it is necessary todeamidate glutamine after protection of the ε-amino group with areversible protecting group such as citraconyl group, to remove theprotecting group thereafter and then to separate the deamidated proteinfrom the released citraconic acid. It is evident that these stepssharply increase the production cost and are far from the realization.

In the case of the peptideglutaminase method, on the other hand, it isnecessary to use a protein hydrolysate, because this enzyme hardlyreacts upon protein but acts only upon a low molecular weight peptideand cannot therefore be applied to raw protein.

In consequence, though the reaction selectivity due to high substratespecificity of enzymes is originally one of the greatest advantages ofthe enzymatic method, which surpasses chemical and physical methods, itis the present situation that the enzymatic method cannot be put intopractical use for the purpose of effecting deamidation of proteinbecause of the absence of an enzyme which does not generate sidereactions and is suited for the deamidation of high molecular weightprotein.

Thus, though the deamidation of protein is an excellent modificationmethod which will result in the great functional improvement, both ofthe conventional chemical and enzymatic methods have disadvantages, andtheir realization therefore is not completed yet.

SUMMARY OF THE INVENTION

In view of the above, the inventors of the present invention haveconducted extensive studies on the screening of an inexpensivemicroorganism to be used as the source of an enzyme capable of directlyacting upon amido groups which are bonded to protein and therebyeffecting deamidation of the protein and, as a result, found that a newstrain belonging to the genus Chryseobacterium, newly isolated from asoil sample by the present inventors, can produce an enzyme which exertsthe deamidation function by directly acting upon amido groups in thebonded state in protein without accompanying cutting of peptid bondingand cross-linking of protein molecules. The present invention has beenaccomplished on the basis of this finding. In this specification, anenzyme which has the aforementioned actions is called a“protein-deamidating enzyme”.

Thereafter, the present inventors have selected strains belonging to thegenus Chryseobacterium randomly from type cultures and examined theirability to produce the protein-deamidating enzyme. As the results, theproductivity of this enzyme was found in all of the selected strains, aswell as in other strains which belong, for example, to the generaFlavobacterium, Empedobacter, Sphingobacterium, Aureobacterium andMyroides. Each of these strains is a bacterium classified intoCytophagales or Actinomycetes, and the bacteria belong to the genusChryseobacterium, Empedobacter, Flavobacterium, and Myroides areclassified into Flavobacteriaceae.

The present inventors have then isolated and purified theprotein-deamidating enzyme, determined nucleotide sequence of the genecoding for said protein-deamidating enzyme and confirmed that theprotein-deamidating enzyme can be produced using a transformanttransformed with a vector containing said gene.

Accordingly, the present invention relates to a method for theproduction of a protein-deamidating enzyme using a microorganism capableof producing the protein-deamidating enzyme, a method for themodification of protein using the protein-deamidating enzyme, acomposition for use in the modification of protein, which comprises theprotein-deamidating enzyme as the active ingredient, a method for theimprovement of functionality of protein using the protein-deamidatingenzyme, a method for the improvement of functionality of food using theprotein-deamidating enzyme, a method for the improvement of extractionefficiency of protein and/or peptide using the protein-deamidatingenzyme and a method for the control of transglutaminase reaction usingthe protein-deamidating enzyme.

The present invention also relates to a protein-deamidating enzyme, agene which encodes said enzyme, a vector which contains said gene, atransformant transformed with said vector and a method for theproduction of the protein-deamidating enzyme, which comprises culturingsaid transformant in a medium, thereby allowing the transformant toproduce the protein-deamidating enzyme, and subsequently collecting theprotein-deamidating enzyme from the culture mixture, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing time course of the culturing ofChryseobacterium gleum JCM 2410 in lactose medium, in which the opensquare indicates changes in pH, the cross indicates changes in theabsorbance of culture medium at 660 nm, the open triangle indicateschanges in the protease activity when casein is used as the substrate,the closed circle indicates changes in the protein-deamidating enzymeactivity when Z-Gln-Gly is used as the substrate and closed triangleindicates changes in the protein-deamidating enzyme activity when caseinis used as the substrate.

FIG. 2 is a graph showing optimum pH of the protein-deamidating enzymeobtained from Chryseobacterium gleum JCM 2410.

FIG. 3 is a graph showing optimum temperature of the protein-deamidatingenzyme obtained from Chryseobacterium gleum JCM 2410.

FIG. 4 is a graph showing pH stability of the protein-deamidating enzymeobtained from Chryseobacteriuum gleum JCM 2410.

FIG. 5 is a graph showing temperature stability of theprotein-deamidating enzyme obtained from Chryseobacterium gleum JCM2410.

FIG. 6 is a graph showing time course of the culturing ofChryseobacterium indologenes IFO 14944 in lactose medium, in which theopen square indicates changes in pH, the cross indicates changes in theabsorbance of culture medium at 660 nm, the open triangle indicateschanges in the protease activity when casein is used as the substrate,the closed circle indicates changes in the protein-deamidating enzymeactivity when Z-Gln-Gly is used as the substrate and closed triangleindicates changes in the protein-deamidating enzyme activity when caseinis used as the substrate.

FIG. 7 is a graph showing time course of the culturing ofChryseobacterium meningosepticum IFO 12535 in lactose medium, in whichthe open square indicates changes in pH, the cross indicates changes inthe absorbance of culture medium at 660 nm, the open triangle indicateschanges in the protease activity when casein is used as the substrate,the closed circle indicates changes in the protein-deamidating enzymeactivity when Z-Gln-Gly is used as the substrate and closed triangleindicates changes in the protein-deamidating enzyme activity when caseinis used as the substrate.

FIG. 8 is a graph showing time course of the culturing ofChryseobacterium balustinum IFO 15053 in lactose medium, in which theopen square indicates changes in pH, the cross indicates changes in theabsorbance of culture medium at 660 nm, the open triangle indicateschanges in the protease activity when casein is used as the substrate,the closed circle indicates changes in the protein-deamidating enzymeactivity when Z-Gln-Gly is used as the substrate and closed triangleindicates changes in the protein-deamidating enzyme activity when caseinis used as the substrate.

FIG. 9 is a photograph showing results of SDS-polyacrylamide gelelectrophoresis in Example 9 using samples in respective steps ofprotein-deamidating enzyme purification.

FIG. 10 is a graph showing releasing pattern of ammonia in Example 11,in which the open triangle indicates results when theprotein-deamidating enzyme was added and the closed triangle indicatesresults of blank test.

FIG. 11 is a graph showing dispersibility of deamidated gluten inExample 12, in which the closed square indicates results of glutentreated with the protein-deamidating enzyme and the closed circleindicates results of untreated gluten.

FIG. 12 is a graph showing solubility of deamidated gluten in Example12, in which the closed square indicates results of gluten treated withthe protein-deamidating enzyme and the closed circle indicates resultsof untreated gluten.

FIG. 13 is a graph showing releasing pattern of ammonia in Example 18,in which the open circle indicates results when the protein-deamidatingenzyme was added and the closed circle indicates results of blank test.

FIG. 14 is a photograph showing results of SDS-polyacrylamide gelelectrophoresis of deamidated casein in Example 18.

FIG. 15 is a graph showing calcium-dependent solubility of deamidatedcasein in Example 19, in which the closed square indicates results ofcasein treated with the protein-deamidating enzyme and the closed circleindicates results of untreated casein.

FIG. 16 is a photograph showing results of SDS-polyacrylamide gelelectrophoresis in Example 23 in which protein-deamidating enzyme wasadded during the reaction by transglutaminase.

FIG. 17 is a photograph showing results of SDS-polyacrylamide gelelectrophoresis of deamidated casein teated with transglutaminase inExample 23.

FIG. 18 is a photograph showing dispersibility and solubility ofdeamidated casein in Example 25, in which the closed square indicatesresults of casein treated with the protein-deamidating enzyme and theclosed circle indicates results of untreated casein.

DETAILED DESCRIPTION OF THE INVENTION

The protein-deamidating enzyme of the present invention acts on theamido group of asparagine residue or glutamine residue in proteins butthe moiety on which this enzyme acts is not particularly limited. Forexample, the protein-deamidating enzyme of the present invention can beeffective on the amido group connected to other amino acids. The term“protein” as used herein is not limited to simple protein but alsoincludes protein complexes, conjugated proteins with saccharides,lipids, etc., and the like. The molecular weight of the protein is notparticularly limited and generally in the range of from 5000 or more andpreferably in the range of from 10,000 to 2,000,000.

The protein-deamidating enzyme of the present invention can be used alsofor deamidation of peptides having an amido group, derivatives thereof,and the like. Examples of the peptides include those having amino acidresidues of 2 to 50. Peptides used as nutrition-improving agents arepreferable.

Thus, the protein-deamidating enzyme of the present invention can act onsubstrates from dipeptides to high molecular weight proteins, includingpolypeptides. Incidentally, the term “polypeptides” as used in thisspecification includes proteins.

A microorganism capable of producing the protein-deamidating enzyme ofthe present invention can be screened, for example, in the followingmanner. That is, an enrichment culturing is carried out by inoculating asoil suspension into an isolation liquid medium containing Z-Gln-Gly asthe sole nitrogen source, the culture broth is spread and cultured on anisolation plate agar medium having the same composition, and thencolonies grown on the medium are selected and picked up. A strain havingthe ability to release ammonia from Z-Gln-Gly can be selected byculturing these colonies in an appropriate liquid medium.

A microorganism capable of producing the protein-deamidating enzyme canbe screened from the thus selected strains using casein as the substrateand ammonia-releasing activity as an index.

A strain screened in this manner was identified as a species belongingto the genus Chryseobacteriumn in accordance with Bergey's Manual ofDeterminative Bacteriology. In addition, it was confirmed by theaforementioned testing method that strains selected at random from typecultures of the genus Chryseobacterium can produce theprotein-deamidating enzyme. Illustrative examples of such strainsinclude Chryseobacterium gleum JCM 2410, Chryseobacterium indologenesIFO 14944, Chryseobacterium meningosepticum IFO 12535, Chryseobacteriumbalustinum IFO 15053, Chryseobacterium indoltheticum ATCC 27950, andChryseobacterium scophthalnum CCM4109.

When other microorganisms are subjected to the same screening method,production of the protein-deamidating enzyme was confirmed in strainsbelonging to the genus Flavobacterium, more illustrativelyFlavobacterium aquatile IFO 15052, the genus Empedobacter, moreillustratively Empedobacter brevis IFO 14943, the genusSphingobacterium, more illustratively Sphingobacterium spiritivorum IFO14948 and Sphingobacterium heparinum IFO 12017, the genusAureobacterium, more illustratively Aureobacterium esteraromatidum IFO3751 and the genus Myroides, more illustratively Myroides odoratus IFO14945.

In this connection, this enzyme can be distinguished from knowntransglutaminase, because it does not have the activity to catalyzeformation of isopeptide between glutamine residue and lysine residue inprotein, namely transglutaminase activity. It can also be distinguishedfrom known protease, because it does not have the activity to hydrolyzepeptide bond of protein, namely protease activity.

Regarding the culturing method of each of the aforementioned strains forthe production of the protein-deamidating enzyme, either a liquidculturing or a solid culturing, but preferably a liquid culturing, maybe used. For example, the liquid culturing can be carried out in thefollowing manner.

Any medium can be used with the proviso that a microorganism capable ofproducing the protein-deamidating enzyme can grow in the medium.Examples of the medium to be used include those which contain carbonsources such as glucose, sucrose, glycerol, dextrin, molasses andorganic acids, nitrogen sources such as ammonium sulfate, ammoniumcarbonate, ammonium phosphate, ammonium acetate, peptone, yeast extract,corn steep liquor, casein hydrolysate and beef extract and inorganicsalts such as potassium salts, magnesium salts, sodium salts, phosphoricacid salts, manganese salts, iron salts and zinc salts.

The medium pH is adjusted to a value of approximately from 3 to 10,preferably from about 7 to 8, and the culturing is carried out underaerobic conditions at a temperature of generally from about 10 to 50°C., preferably from about 20 to 37° C., for a period of from 1 to 20days, preferably from 3 to 12 days. As the culturing method, a shakingculture method or an aerobic submerged jar fermentor culture method maybe used.

The protein-deamidating enzyme of the present invention can be obtainedby isolating the protein-deamidating enzyme from the thus obtainedculture broth in the usual way. For example, when theprotein-deamidating enzyme is isolated and purified from the culturebroth, purified protein-deamidating enzyme can be obtained by treatingit in the usual way by the combination of centrifugation, UFconcentration, salting out and various types of chromatography such asof an ion exchange resin.

The present invention is described more illustratively. That is, theaforementioned Chryseobacterium gleum JCM 2410 was used as aprotein-deamidating enzyme producing strain and cultured in a liquidmedium, and production, purification and properties of the enzyme wereexamined.

One loopful of cells grown on a fresh slant medium were inoculated intothe following lactose medium and cultured on a shaker at 30° C. for 2 to7 days, and then centrifugation supernatant is obtained. Lactose mediumcomposition (pH 7.2)

Lactose (manufactured by Wako Pure Chemical  0.5% Industries)Polypeptone (manufactured by Wako Pure Chemical  1.0% Industries)Na₂HPO₄.H₂O  0.17% KH₂PO₄ 0.025% MgSO₄.7H₂O 0.025% FeSO₄.7H₂O 0.005%

Time course of the culturing is shown in FIG. 1.

After completion of the culturing, the enzyme of interest was purifiedby subjecting the culture broth to centrifugation (12,000 rpm, 4° C., 20minutes) to obtain the supernatant as a crude enzyme solution, andtreating the thus obtained solution by UF concentration (SEP-0013),salting out, Phenyl-Sepharose and Sephacyl S-100. Steps of thepurification are shown in Table 1.

TABLE 1 Total Total Specific Recovery protein activity activity Yield mgU U/mg % Culture broth 83.50 16.53 0.198 100 UF concentration 11.7813.17 1.12 79.7 Salting out 4.10 10.03 4.09 60.7 Phenyl-Sepharose 0.1873.10 16.6 18.7 Sephacyl S-100 0.073 2.26 31.1 13.7

In this connection, measurement of the enzyme activity was carried outin the following manner using Z-Gln-Gly and casein as substrates.

Activity measuring method: A 10 μl portion of each enzyme solution isadded to 100 μl of 176 mM phosphate buffer (pH 6.5) containing 10 mMZ-Gln-Gly and incubated at 37° C. for 60 minutes, and then the reactionis stopped by adding 100 μl of 12% trichloroacetic acid solution. Aftercentrifugation (15,000 rpm, 4° C., 5 minutes), the resulting supernatantis measured in the following manner using F-kit ammonia (manufactured byBoehringer-Mannheim) (A1). Separately, the same measurement is carriedout using water instead of the enzyme solution (A2).

F-Kit Ammonia

A 10 μl portion of the supernatant and 190 μl of water are added to 100μl of Reagent 2, the resulting mixture is allowed to stand at roomtemperature for 5 minutes and then the absorbance of 100 μl portion ofthe reaction solution is measured at 340 nm (E1). The remaining 200 μlportion is mixed with 1.0 μl of Reagent 3 (glutamate dehydrogenase),allowed to stand at room temperature for 20 minutes and then theabsorbance of the remaining 200 μl is measured at 340 nm (E2).

The amount of enzyme which releases 1 μmol of ammonia within one minuteunder the above reaction conditions is defined as one unit andcalculated based on the following formula.U/ml=1.76×[A1(E1−E2)−A2(E1−E2)]

Using 1% casein (Hermastein, manufactured by Merck) instead of 10 mMZ-Gln-Gly as the substrate, the activity is measured in the same mannerto confirm that the enzyme acts upon amino groups bonded to the protein.In this case, the protease activity was also checked by measuring theabsorbance of the centrifugation supernatant after termination of thereaction at 280 nm. The amount of enzyme which increases 10 D unitsunder this condition was defined as one unit of protease activity.

In addition, glutaminase activity was measured by the similar methodexcept that 10 mM glutamine was used as the substrate instead of 10 mMZ-Gln-Gly.

Transglutaminase activity was measured by the following hydroxamic acidmethod using Z-Gln-Gly as the substrate.

Reagent A 0.2 M Tris-HCl buffer (pH 6.0) 0.1 M hydroxylamine 0.01 Mreduced glutathione 0.03 M benzyloxycarbonyl-L-glutaminylglycine ReagentB 3 N hydrochloric acid 12% trichloroacetic acid 5% FeCl₃•6H₂O(dissolved in 0.1 M HCl)

A 1:1:1 mixture of these solutions is used as reagent B.

A 0.05 ml portion of each enzyme solution is mixed with 0.5 ml of thereagent A to carry out 10 minutes of the reaction at 37° C., thereaction solution is mixed with 0.5 ml of the reagent B to stop thereaction and to effect formation of Fe complex, and then the absorbanceat 525 nm is measured. As a control, the same reaction is carried outusing the same enzyme solution heat-inactivated in advance, and theabsorbance is measured to calculate its difference from the absorbanceof the intact enzyme solution. Separately from this, a calibration curveis prepared using L-glutamic acid γ-monohydroxamate instead of theenzyme solution, for use in the calculation of the amount of formedhydroxamic acid based on the just described difference in absorbance,and the enzyme activity which forms 1 μmol of hydroxamic acid within oneminute is defined as one unit.

In this connection, the amount of protein was determined using BCAProtein Assay Kit (manufactured by Pierce) and bovine serum albumin asthe standard protein.

(1) Measurement of molecular weight: 20 kDa as determined bySDS-polyacrylamide gel electrophoresis.

(2) Measurement of optimum pH: A 100 μl portion of 40 mMBritton-Robinson buffer solution (having a pH value of from 3 to 12)containing 10 mM Z-Gln-Gly was pre-incubated at 37° C. for 5 minutes, 10μl of each enzyme solution containing 0.32 μg of the protein-deamidatingenzyme was added to the buffer and incubated at 37° C. for 60 minutes tomeasure the enzyme activity. The results are shown in FIG. 2.

(3) Measurement of optimum temperature: A 10 μl portion of enzymesolution containing 1.21 μg of the protein-deamidating enzyme was addedto 100 μl of a substrate solution [176 mM phosphate buffer (pH 6.5)containing 10 mM Z-Gln-Gly], and the reaction was carried out at eachtemperature for 60 minutes to measure the enzyme activity. The resultsare shown in FIG. 3.

(4) Measurement of pH stability: A 22 μl portion of enzyme solutioncontaining 0.75 μg of the protein-deamidating enzyme (in 40 mMBritton-Robinson buffer solution having a pH value of from 3 to 12) wastreated at 30° C. for 18 hours. Thereafter, the remaining enzymeactivity was measured. The results are shown in FIG. 4.

(5) Measurement of temperature stability: A 43 μl portion of enzymesolution containing 1.76 μg of the protein-deamidating enzyme [in 50 mMphosphate buffer solution (pH 7.0)] was allowed to stand at eachtemperature for 10 minutes, and then the remaining enzyme activity wasmeasured. The results are shown in FIG. 5.

(6) Substrate specificity: A 100 μl portion of each of 1% solutions ofvarious proteins used as the substrates was mixed with 10 μl of aprotein-deamidating enzyme solution (10 mU), and 18 hours of thereaction was carried out at 37° C. As a control, the same treatment wascarried out using water instead of the enzyme solution, and the amountof released ammonia was measured. The amount of released ammonia whenwater was added was subtracted from the amount of released ammonia whenthe enzyme solution was added, with the results shown in Table 2. When aportion of the reaction mixture after completion of the reaction wassubjected to SDS-PAGE and compared with the control, increased ordecreased molecular weight of the protein was not found. This resultmeans that the enzyme of the present invention is a novel enzyme whichcan be distinguished from known transglutaminase and protease.

TABLE 2 Protein Released ammonia (mM) Casein 2.45 Gluten 1.85 Soybeanpowder 0.10 Corn meal 0.12 β-Lactoglobulin 0.65 Ovalbumin 0.24

(7) Measurement of isoelectric point: The isoelectric point was measuredby the electrofocusing using Ampholine (600 V, 4° C., 48 hours). As aresult, the enzyme of the present invention had an isoelectric point of10.2.

Next, the method of the present invention for the modification ofprotein using the aforementioned protein-deamidating enzyme is describedin detail.

The protein-deamidating enzyme of the present invention is allowed toact upon various proteins. Any type of protein can be used, with theproviso that it undergoes action of the aforementioned enzyme, and itsexamples are plant proteins obtained from beans and cereals and animalproteins which include milk proteins such as casein and β-lactoglobulin,egg proteins such as ovalbumin, meat proteins such as myosin and actin,blood proteins such as serum albumin and tendon proteins such as gelatinand collagen. Also included are partially hydrolyzed proteins obtainedby chemical treatment with an acid or an alktli or by enzymatictreatment (e.g., with a protease), chemically modified proteins withvarious reagents and synthesized peptides.

These substrate proteins are subjected to the reaction in the form ofsolution, slurry or paste, but their concentrations are not particularlylimited and optionally decided depending on the desired properties andconditions of the deamidated protein of interest. Also, the solution,slurry or paste of each substrate protein is not limited to an aqueoussolution and may be in the form of emulsion with oil and fat and, asoccasion demands, may contain additives such as salts, saccharides,proteins, perfumes, moisture keeping agents and coloring agents.

The reaction conditions such as amount of the enzyme, reaction time andtemperature and pH of the reaction solution are not particularly limitedtoo, but the reaction may be generally carried out using the enzyme inan amount of from 0.1 to 100 units, preferably from 1 to 10 units, basedon 1 g of protein, at a reaction temperature of from 5 to 80° C.,preferably from 20 to 60° C., at a reaction solution pH of from 2 to 10,preferably from 4 to 8, and for a period of from 10 seconds to 48 hours,preferably from 10 minutes to 24 hours. In addition, these conditionscan be optionally changed depending, for example, on the purity of theenzyme to be used and the kind and purity of the substrate protein to beused. These reaction conditions are also applied to various uses of theenzyme of the present invention described in the following.

Thus, the action of the protein-deamidating enzyme of the presentinvention upon various proteins renders possible direct deamidation ofamido groups in the protein. As the results, negative charge of the thusdeamidated protein increases, which accompanies reduced pI, increasedhydration ability and increased electrostatic repulsion. Also, changesin the higher-order structure of protein result in the increase ofsurface hydrophobic property. These effects result in the improvement offunctionality of protein, such as increment of solubility anddispersibility, increment of foamability and foam stability andincrement of emulsification ability and emulsification stability.

Thus, the protein having improved functionality greatly expands its usemainly in the field of food. A number of plant proteins show poorfunctionality such as solubility, dispersibility and emulsificationability particularly under weakly acidic condition which is the pH rangeof general food, so that they cannot be used in many food articles whichinclude acidic drinks such as coffee whitener and juice, and dressing,mayonnaise and cream. However, when a plant protein having poorsolubility, such as wheat gluten, is deamidated by the presentinvention, its solubility and dispersibility are increased, so that itsuse in these unsuited food articles becomes possible and it can be usedas tempura powder having high dispersibility.

The enzyme of the present invention can also be used for the improvementof dough in the field of bakery and confectionery. For example, a doughmaterial having high gluten content has problems in terms of handlingand mechanical characteristics of the dough because of its lowextensibility, as well as volume and quality of the finished bread.These problems can be resolved by improving the extensibility throughthe deamidation of gluten with this enzyme. Also, the deamidated glutenshows the effect as an emulsifying agent, so that bread producingcharacteristics such as keeping quality and softness are also improved.In addition, a dough material containing deamidated gluten has lowplasticity and excellent extensibility, so that this is suitable for theproduction of crackers, biscuits, cookies, pizza pies or crusts of pie,and the enzyme of the present invention can be used in their production.For this purpose, the enzyme of the present invention is used generallyin an amount of from 0.01 unit/kg to 10,000 units/kg, preferably from0.1 unit/kg to 150 units/kg, based on the total weight of doughcomprising wheat gluten and water, and they are mixed in the usual way.

Still more, when a protein in food, which causes allergy, anon-resistant disease or a genetic disease, is treated with the enzymeof the present invention, its toxicity and allergenic property can beremoved or reduced. In the case of food allergy, most of the allergenpeptides generally have high hydrophobic property. When they areconverted into hydrophilic peptides by their treatment with the enzymeof the present invention, the allergenic property is removed or reduced.Particularly, large effect can be obtained when an allergen peptidecontains glutamine residue such as the case of a wheat gluten allergen.

Still more, when a protein is deamidated by the enzyme of the presentinvention, mineral-sensitivity of the protein is reduced, so that thesoluble mineral content in a protein-mineral solution is increased andabsorption of minerals in the human body can be improved. It is wellknown in general that absorption of calcium contained in food by thehuman body is improved when calcium is solubilized using an organic acidor casein phosphopeptide. Based on the same mechanism, it is possible tosolubilize a large quantity of calcium by deamidation of the protein bythe enzyme of the present invention. Using the deamidated protein, highmineral (e.g., calcium) containing drinks and a mineral (e.g., calcium)absorption enhancing agents can be produced.

Also, in the case of the production of amino acid based condiments (HAP(Hydrolized Animal Protein) and HVP (Hydrolyzed Vegetable Protein)),bean paste (miso) or soy sauce, other effects such as reduction ofbitterness, improvement of protein hydrolyzing ratio by protease andincrease of the glutamic acid content can be obtained. It is well knownin general that the cause of bitterness is originated from hydrophobicpeptides, so that the deamidation renders possible reduction of bitterpeptides. It is known also that a peptide having glutamic acid on itsN-terminal has the effect to mask bitterness. In addition, since primarystructure and higher-order structure of a material protein are changedby deamidation, protease-sensitivity of the protein can also beincreased. As the results, the low degradation ratio, as a probleminvolved in the enzymatic production of HAP and HVP, can also beimproved. On the other hand, reduction of the glutamic acid contentcaused by the formation of pyroglutamic acid is another problem in theproduction of HAP and HVP. Pyroglutamic acid is formed by theintramolecular cyclization of free glutamine, but it can be prevented bydeamidation of the material protein and, as the result, the glutamicacid content is increased.

Still more, the enzyme of the present invention can be used as an agentfor use in the control of the transglutaminase reaction.Transglutaminase is broadly used as a protein modifying agent, namely asa cross-linking enzyme, in the field of food and other industrialfields. The purpose of the use of transglutaminase is to obtain gelledprotein products by the protein cross-linking reaction of the enzyme orto improve functionality of protein, but it is difficult to obtain aproduct having desired cross-linking degree and functionality inresponse to respective use and object, namely to control thecross-linking reaction such as termination of the reaction at anappropriate stage. Particularly in the case of the modification ofproteins for food use, it is not desirable to add generally knowntransglutaminase inhibitors such as EDTA, ammonium chloride and SHreagents.

It is possible to terminate the transglutaminase reaction by adding theprotein-deamidating enzyme of the present invention at a desired stageduring the reaction of transglutaminase. That is, the transglutaminasereaction can be stopped by converting glutamine residues which are thetarget of the transglutaminase reaction in the substrate protein intoglutamic acid residues by the protein-deamidating enzyme.

In that case, it is necessary that the affinity of theprotein-deamidating enzyme for glutamine residues in a protein as itssubstrate is higher than that of transglutaminase, but the latter caseof reaction requires the ε-amino group of lysine in addition toglutamine residues while the former case requires only water other thanthe glutamine residues, which is abundantly present in the reactionenvironment, so that it is believed that the reaction ofprotein-deamidating enzyme generally precedes the reaction oftransglutaminase. As a matter of course, a modified or gelled proteinhaving desired cross-linking degree can be obtained by appropriatelytreating a substrate protein with the protein-deamidating enzyme toeffect conversion of desired glutamine groups into glutamic acidresidues and then subjecting the thus treated protein to thetransglutaminase reaction.

The protein-deamidating enzyme of the present invention can also be usedas a reagent for use in the functional modification of protein, namelyfor use in protein engineering. When the substrate protein is an enzyme,enzymatic, chemical and physicochemical properties of the enzyme can bemodified. For example, when an enzyme protein is deamidated by theenzyme of the present invention, isoelectric point of the enzyme proteinis reduced so that its pH stability can be modified. Also, otherproperties-of the enzyme such as substrate affinity, substratespecificity, reaction-speed, pH-dependency, temperature-dependency andtemperature stability can be modified by changing the structure orelectric environment of its active site.

It also can be used as reagents for analyses and studies of protein,such as a reagent for use in the determination of amide content ofprotein and a reagent for use in the solubilization of protein.

In addition, the enzyme of the present invention can be used for theimprovement of extraction and concentration efficiencies of cereal andbean proteins. In general, proteins of cereals and beans such as wheatand soybean are mostly insoluble in water and cannot therefore beextracted easily, but such proteins can be extracted easily and highcontent protein isolates can be obtained when these proteins aresolubilized by treating a suspension of wheat flour or soybean flourwith the enzyme of the present invention.

In the case of soybean protein, when the protein is generally extractedfrom defatted soybean powder or flakes (protein content, about 50%), theprotein is firstly insolubilized by a heat treatment, an ethanoltreatment or an isoelectric point treatment at around pH 4.5, and thensoluble polysaccharides are removed to obtain a soybean proteinconcentrate having a protein content of about 70%. When protein of morehigher purity is desired, it is prepared by suspending or dissolvingsoybean powder or the concentrate in a dilute alkali solution todissolve the protein and then removing insoluble substances. Thisproduct is called soybean protein isolate and contains about 90% of theprotein. These soybean protein products are applied to various foodarticles such as ham, sausages and baby food, utilizing emmulsifyingactivity, gelling propety, and water-retaining property as well as highnutrition of the soybean protein

When the enzyme of the present invention is used in producing thesesoybean protein products, not only the yield is improved due to theincreased solubility of protein but also high concentration proteinproducts can be produced. Since the protein products obtained in thismanner are deamidated, they have excellent functionality. Inconsequence, they can exert excellent effects when used in various foodarticles such as meat or fish products and noodles, and their userenders possible production of food articles having new texture andfunctionality.

The following describes the protein-deamidating enzyme of the presentinvention, a gene which encodes the protein-deamidating enzyme, arecombinant vector which contains said gene, a transformant transformedwith said vector and a method for the production of theprotein-deamidating enzyme, which comprises culturing said transformantin a medium, thereby allowing the transformant to produce theprotein-deamidating enzyme, and subsequently collecting theprotein-deamidating enzyme from the culture mixture.

Regarding the protein-deamidating enzyme of the present invention, allof the protein-deamidating enzymes which can be obtained by theaforementioned protein-deamidating enzyme production methods areincluded, in which particularly preferred one is a polypeptide which hasthe amino acid sequence of Sequence No. 6 shown in the Sequence Listingattached, wherein one or more amino acid residues of the amino acidsequence may be modified by at least one of deletion, addition,insertion and substitution, and more preferred one is a polypeptidewhich has the amino acid sequence of Sequence No. 6 shown in theSequence Listing.

Examples of the gene which encodes the protein-deamidating enzyme of thepresent invention include a gene which can be obtained from amicroorganism capable of producing said protein-deamidating enzyme bycloning of said gene and a gene which has a certain degree of homologywith said gene. Regarding the homology, a gene having a homology of atleast 60% or more, preferably a gene having a homology of 80% or moreand more preferably a gene having a homology of 95% or more can beexemplified. The following nucleotide (DNA or RNA) is desirable as thegene which encodes the protein-deamidating enzyme of the presentinvention.

A nucleotide which comprises a nucleotide being selected from thefollowing nucleotides (a) to (g) and encoding a polypeptide having theactivity to deamidate amido groups in protein;

(a) a nucleotide which encode a polypeptide having the amino acidsequence of Sequence No. 6 shown in the Sequence Listing,

(b) a nucleotide which encode a polypeptide having the amino acidsequence of Sequence No. 6 shown in the Sequence Listing, wherein one ormore amino acid residues of the amino acid sequence are modified by atleast one of deletion, addition, insertion and substitution,(c) a nucleotide which has the nucleotide sequence of Sequence No. 5shown in the Sequence Listing,(d) a nucleotide which has the nucleotide sequence of Sequence No. 5shown in the Sequence Listing, wherein one or more bases of thenucleotide sequence are modified by at least one of deletion, addition,insertion and substitution,(e) a gene which hybridizes with any one of the aforementionednucleotides (a) to (d) under a stringent condition,(f) a nucleotide which has homology with any one of the aforementionednucleotides (a) to (d), and(g) a nucleotide which is degenerate with respect to any one of theaforementioned nucleotides (a) to (f).

The gene which encodes the protein-deamidating enzyme of the presentinvention can be prepared from the aforementioned microorganism capableof producing the protein-deamidating enzyme by carrying out cloning ofsaid gene in the following manner. Firstly, the protein-deamidatingenzyme of the present invention is isolated and purified from amicroorganism capable of producing the protein-deamidating enzyme by theaforementioned method and information on its partial amino acid sequenceis obtained.

Regarding the determination method of a partial amino acid sequence, itis effective to carry out a method in which purified protein-deamidatingenzyme is directly applied to an amino acid sequence analyzer (such asProtein Sequenser 476A, manufactured by Applied Biosystems) by Edmandegradation method [J. Biol. Chem., vol. 256, pp. 7990-7997 (1981)], ora method in which limited hydrolysis of the protein-deamidating enzymeis carried out using a proteolytic enzyme, the thus obtained peptidefragments are isolated and purified and then amino acid sequences of thethus purified peptide fragments are analyzed.

Based on the information of the thus obtained partial amino acidsequences, the protein-deamidating enzyme gene is cloned. In general,the cloning is carried out making use of a PCR method or a hybridizationmethod.

When a hybridization method is used, the method described in “MolecularCloning, A Laboratory Manual” (edit. by T. Maniatis et al., Cold SpringHarbor Laboratory, 1989) may be used.

When a PCR method is used, the following method can be used.

Firstly, a gene fragment of interest is obtained by carrying out PCRreaction using genomic DNA of a microorganism capable of producing theprotein-deamidating enzyme as the template and synthetic oligonucleotideprimers designed based on the information of partial amino acidsequences. The PCR method is carried out in accordance with the methoddescribed in “PCR Technology” (edit. by Erlich H. A., Stockton Press,1989). When nucleotide sequences of the thus amplified DNA fragments aredetermined by a generally used method such as the dideoxy chaintermination method, a sequence which corresponds to the partial aminoacid sequence of the protein-deamidating enzyme is found in the thusdetermined sequences, in addition to the sequences of syntheticoligonucleotide primers, so that a part of the protein-deamidatingenzyme gene of interest can be obtained. As a matter of course, a genewhich encodes complete protein-deamidating enzyme can be cloned byfurther carrying out a cloning method such as the hybridization methodusing the thus obtained gene fragment as a probe.

In Example 26 of this specification, a gene coding for theprotein-deamidating enzyme was determined by the PCR method usingChryseobacterium gleum JCM 2410. Complete nucleotide sequence of thegene coding for the protein-deamidating enzyme originated fromChryseobacterium gleum JCM 2410 is shown in the Sequence No. 5, and theamino acid sequence encoded thereby was determined to be the sequenceshown in the Sequence No. 6. In this connection, there are countlessnucleotide sequences which correspond to the amino acid sequence shownin the sequence No. 6, in addition to the nucleotide sequence shown inthe Sequence No. 5, and all of these sequences are included in the scopeof the present invention.

The gene of interest can also be obtained by chemical synthesis based onthe information of the amino acid sequence shown in the Sequence No. 6and the nucleotide sequence shown in the Sequence No. 5 (cf. Gene,60(1), 115-127, (1987)).

Regarding the protein-deamidating enzyme gene of the present invention,a nucleotide which encode a polypeptide having the amino acid sequenceof Sequence No. 6 shown in the Sequence Listing, wherein one or moreamino acid residues of the amino acid sequence are modified by at leastone of deletion, addition, insertion and substitution, a gene whichhybridizes with said nucleotide under a stringent condition, anucleotide which has homology with said nucleotide and a nucleotidewhich is degenerate with respect to said nucleotide are also included inthe present invention, with the proviso that the polypeptides encodedthereby have the protein-deamidating enzyme activity.

The term “under stringent condition” as used herein means the followingcondition. That is, a condition in which the reaction system isincubated at a temperature of from 50 to 65° C. for a period of from 4hour to overnight in 6×SSC (1×SSC is a solution composed of 0.15 M NaCland 0.015 M citric acid, pH 7.0) containing 0.5% SDS, 5×Denhart's (asolution composed of 0.1% bovine serum albumin (BSA), 0.1% polyvinylpyrrolidone and 0.1% Ficoll 400) and 100 μg/ml of salmon sperm DNA.

By using the entire portion or a part of the protein-deamidating enzymegene, whose complete nucleotide sequence has been revealed making use ofChryseobacterium gleum JCM 2410, as a probe for hybridization, DNAfragments having high homology with the protein-deamidating enzyme geneof Sequence No. 5 can be selected from genomic DNA libraries or cDNAlibraries of microorganisms capable of producing otherprotein-deamidating enzymes.

The hybridization can be carried out under the aforementioned stringentcondition. For example, a genomic DNA library or a cDNA library obtainedfrom a microorganism capable of producing a protein-deamidating enzymeis fixed on a nylon membrane, and the thus prepared nylon membrane issubjected to blocking at 65° C. in a pre-hybridization solutioncontaining 6×SSC, 0.5% SDS, 5×Denhart's and 100 μg/ml of salmon spermDNA. Thereafter, each probe labeled with ³²P is added to the nylonmembrane which is then incubated overnight at 65° C. The thus treatednylon membrane is washed in 6×SSC at room temperature for 10 minutes, in2×SSC containing 0.1% SDS at room temperature for 10 minutes and then in0.2×SSC containing 0.1% SDS at 45° C. for 30 minutes, subsequentlysubjecting the thus washed membrane to an auto-radiography to detect aDNA fragment which hybridizes with the probe in a specific fashion.Also, genes which show various degree of homology can be obtained bychanging certain conditions such as washing.

On the other hand, primers for use in the PCR reaction can be designedfrom the nucleotide sequence of the gene of the present invention. Bycarrying out the PCR reaction using these primers, gene fragments havinghigh homology with the gene of the present invention can be detected andthe complete gene can also be obtained.

In order to determine whether the thus obtained gene encodes apolypeptide having the protein-deamidating enzyme activity of interest,the thus determined nucleotide sequence is compared with the nucleotidesequence coding for the protein-deamidating enzyme of the presentinvention or with its amino acid sequence, and the identity is estimatedbased on the gene structure and homology. Alternatively, it is possibleto determine whether the gene encodes a polypeptide which has theprotein-deamidating enzyme activity of interest by producing apolypeptide of the gene and measuring its the protein-deamidating enzymeactivity.

The following method is convenient for producing a polypeptide havingthe protein-deamidating enzyme activity using the protein-deamidatingenzyme gene of the present invention.

Firstly, transformation of a host is carried out using a vectorcontaining the protein-deamidating enzyme gene of interest and thenculturing of the thus obtained transformant is carried out undergenerally used conditions, thereby allowing the strain to produce apolypeptide having the protein-deamidating enzyme activity.

Examples of the host to be used include microorganisms, animal cells andplant cells. Examples of the microorganisms include Escherichia coli,microorganisms belonging to the genus Bacillus, Streptomyces,Lactococcus, etc., yeasts belonging to the genus Saccharomyces, Pichia,Kluyveromyces, etc., and filamentous fungi belonging to the genus,Aspergillus, Penicillium, Trichoderma, etc. Examples of animal cellsinclude animal cells utilizing the baculovirus expression system.

Confirmation of the expression and expressed product can be made easilyby the use of an antibody specific for the protein-deamidating enzyme,and the expression can also be confirmed by measuring theprotein-deamidating enzyme activity.

As described in the foregoing, purification of the protein-deamidatingenzyme from the transformant culture medium can be carried out byoptional combination of centrifugation, UF concentration, salting outand various types of chromatography such as of ion exchange resins.

In addition, since the primary structure and gene structure of theprotein-deamidating enzyme have been revealed by the present invention,it is possible to obtain a gene coding for the amino acid sequence of anatural protein-deamidating enzyme, in which one or more amino acidresidues of the amino acid sequence are modified by at least one ofdeletion, addition, insertion and substitution, by introducing randommutation or site-specific mutation using the gene of the presentinvention. This method renders possible preparation of a gene coding fora protein-deamidating enzyme which has the protein-deamidating enzymeactivity but its properties such as optimum temperature, temperaturestability, optimum pH and pH stability, substrate specifivity, etc. areslightly changed, and it also renders possible production of suchprotein-deamidating enzymes by means of gene engineering techniques.

Examples of the method for introducing random mutation include achemical DNA treating method in which a transition mutation is inducedto convert cytosine base into uracil base by the action of sodiumhydrogensulfite [Proceedings of the National Academy of Sciences of theUSA, vol. 79, pp. 1408-1412 (1982)], a biochemical method in which basesubstitution is induced during the step of double strand formation inthe presence of [α-S] dNTP [Gene, vol. 64, pp. 313-319 (1988)] and a PCRmethod in which PCR is carried out by adding manganese to the reactionsystem to decrease accuracy of the nucleotide incorporation [AnalyticalBiochemistry, vol. 224, pp. 347-353 (1995)].

Examples of the method for introducing site-specific mutation include amethod in which amber mutation is employed [gapped duplex method;Nucleic Acids Research, vol. 12, no. 24, pp. 9441-9456 (1984)], a methodin which recognition sites of restriction enzymes are used [AnalyticalBiochemistry, vol. 200, pp. 81-88 (1992); Gene, vol. 102, pp. 67-70(1991)], a method in which mutation of dut (dUTPase) and ung (uracil DNAglycosylase) is used [Kunkel method; Proceedings of the National Academyof Sciences of the USA, vol. 82, pp. 488-492 (1985)], a method in whichamber mutation is induced using DNA polymerase and DNA ligase[oligonucleotide-directed dual amber (ODA) method: Gene, vol. 152, pp.271-275 (1995); JP-A-7-289262 (the term “JP-A” used herein means anunexamined published Japanese patent application)], a method in which ahost introduced with a DNA repair system is used (JP-A-8-70874), amethod in which a protein capable of catalyzing DNA chain exchangereaction is used (JP-A-8-140685), a method in which PCR is carried outusing two different primers for mutation use to which recognition sitesof restriction enzymes are added (U.S. Pat. No. 5,512,463), a method inwhich PCR is carried out using a double-stranded DNA vector having aninactivated drug resistance gene and two different primers [Gene, vol.103, pp. 73-77 (1991)] and a method in which PCR is carried out makinguse of amber mutation (WO 98/02535).

Also, site-specific mutation can be introduced easily by the use ofcommercially available kits. Examples of such kits include Mutan™-G(manufactured by Takara Shuzo) in which the gapped duplex method isused, Mutan™-K (manufactured by Takara Shuzo) in which the Kunkel methodis used, Mutan™-Express Km (manufactured by Takara Shuzo) in which theODA method is used and QuickChange™ Site-Directed Mutagenesis Kit(manufactured by STRATAGENE) in which primers for mutation use andPyrococcus furiosus DNA polymerase are used, as well as TaKaRa LA PCR invitro Mutagenesis Kit (manufactured by Takara Shuzo) and Mutan™ SuperExpress Km (manufactured by Takara Shuzo) as kits in which PCR is used.

Thus, the primary structure and gene structure of theprotein-deamidating enzyme provided by the present invention renderpossible production of an inexpensive and high purity polypeptide havingthe protein-deamidating enzyme activity by means of gene engineeringtechniques.

In this connection, various literature and references are cited in thespecification, and all of them are incorporated herein by references.

Examples of the present invention are given below by way of illustrationand not by way of limitation. Unless otherwise noted, the term “%” usedin the following means “W/V %”.

EXAMPLE 1

Chryseobacterium gleum JCM 2410 was cultured on a shaker at 30° C. for 6days using the aforementioned lactose medium. Time course of theculturing is shown in FIG. 1.

EXAMPLE 2

Chryseobacterium indologenes IFO 14944, Chryseobacterium meningosepticumIFO 12535 and Chryseobacterium balustinum IFO 15053 were cultured in thesame manner as described in Example 1. Time courses of their culturingare shown in FIGS. 6 to 8.

EXAMPLE 3

Flavobacterium aquatile IFO 15052 was cultured in the same manner asdescribed in Example 1. The protein-deamidating enzyme activity in theculture broth is shown in Table 3.

EXAMPLE 4

Empedobacter brevis IFO 14943 was cultured in the same manner asdescribed in Example 1. The protein-deamidating enzyme activity in theculture broth is shown in Table 3.

EXAMPLE 5

Sphingobacterium spiritivorum IFO 14948 and Sphingobacterium heparinumIFO 12017 were cultured in the same manner as described in Example 1.The protein-deamidating enzyme activity in the culture broth is shown inTable 3.

EXAMPLE 6

Aureobacterium esteroaromaticum IFO 3751 was cultured in the same manneras described in Example 1. The protein-deamidating enzyme activity inthe culture broth is shown in Table 3.

EXAMPLE 7

Myroides odoratus IFO 14945 was cultured in the same manner as describedin Example 1. The protein-deamidating enzyme activity in the culturebroth is shown in Table 3.

TABLE 3 Culture Deamidation time activity (U/ml) Strain (h) Z-Gln-GlyCasein Flavobacterium 48 0.019 0.038 aquatile IFO 15052 Empedobacter 200.040 0.149 brevis IFO 14943 Sphingobacterium 20 0.057 0.078spiritivorum IFO 14948 Sphingobacterium 48 0.047 0.031 heparinum IFO12017 Aureobacterium 31 0.003 0.019 esteroaromaticum IFO 3751 Myroides41 0.005 0.026 odoratus IFO 14945

Production of the protein-deamidating enzyme was confirmed in each ofthe strains used in Examples 1 to 7.

EXAMPLE 8

When the strains used in Examples 1 to 5 were cultured in the samemanner using the following medium instead of the lactose medium,production of the protein-deamidating enzyme was found in each strain.

Yeast extract 0.25% Polypeptone  0.3% Casein sodium 0.25% Na₂HPO₄.12H₂O 0.3% MgSO₄.7H₂O 0.02% (pH 7.0)

EXAMPLE 9

The culture broth obtained after 24 hours of culturing in Example 1 wassubjected to 15 minutes of centrifugation at 4° C. and at 12,000 rpm(22,200×g) to remove cells, and the thus obtained centrifugationsupernatant was concentrated to about 17 times using an ultrafiltrationmembrane (SEP-0013, manufactured by Asahi Chemical Industry) and thendialyzed overnight at 4° C. against 10 mM sodium phosphate buffersolution (pH 6.5) containing 2.0 M NaCl. The thus formed precipitate wasremoved by 15 minutes of centrifugation at 4° C. and at 10,000 rpm(12,300 ×g), and the thus obtained centrifugation supernatant wasapplied to a Phenyl-Sepharose CL-6B column (manufactured by Pharmacia)which had been equilibrated with 10 mM sodium phosphate buffer solution(pH 6.5) containing 2.0 M NaCl, and the adsorbed protein was eluted by alinear NaCl density gradient of from 2.0 M to 0 M.

Fractions having protein deamidation activity were combined,concentrated using the ultrafiltration membrane and then applied to aSephacryl S-100 column which had been equilibrated with 10 mM sodiumphosphate buffer solution (pH 6.5) containing 0.6 M NaCl and 0.05% Tween20, and the elution was carried out using the same buffer. Fractionshaving protein deamidation activity were combined, concentrated usingthe ultrafiltration membrane and then dialyzed against distilled water,thereby obtaining a protein-deamidating enzyme solution.

Samples of purification steps were subjected to 10-20%SDS-polyacrylamide gel electrophoresis. The result is shown in FIG. 9.It is apparent that the purified enzyme sample (lane 5) is a singleprotein having a molecular weight of about 20 kDa by SDS-polyacrylamidegel electrophoresis.

When measured by the aforementioned assay methods (the method which usesZ-Gln-Gly as the substrate and the method which uses casein as thesubstrate), the thus obtained enzyme preparation showed the activitiesof 18.8 units/ml (Z-Gln-Gly as the substrate) and 14.0 units/ml (caseinas the substrate). Transglutaminase activity and protease activity werenot detected. In consequence, it is evident that the protease activityin the culture broth shown in FIG. 1 was completely removed by theaforementioned purification process. In addition, the enzyme preparationdid not show glutaminase activity against free glutamine.

EXAMPLE 10

Each culture broth obtained in Examples 2 to 7 was purified in the samemanner as described in Example 9. As a result, respective activitiesshown in Table 4 were obtained. Transglutaminase activity and proteaseactivity were not detected in the thus obtained protein-deamidatingenzymes. In consequence, it is evident that the protease activity in theculture broth was completely removed by the aforementioned purificationprocess.

TABLE 4 Deamidation activity (U/ml) Strain Z-Gln-Gly CaseinChryseobacterium 14.2 10.5 indologenes IFO 14944 Chryseobacterium 13.210.3 meningosepticum IFO 12535 Chryseobacterium 9.88 7.48 balustinum IFO15053 Flavobacterium 3.97 3.09 aquatile IFO 15052 Empedobacter 2.11 1.48brevis IFO 14943 Sphingobacterium 1.59 1.25 spiritivorum IFO 14948Sphingobacterium 7.43 5.20 heparinum IFO 12017 Aureobacterium 1.44 1.15esteroaromaticum IFO 3751 Myroides 3.06 2.36 odoratus IFO 14945

EXAMPLE 11

Preparation of Deamidated Gluten

A 1 g portion of wheat gluten was suspended in 100 ml of 176 mM sodiumphosphate buffer (pH 6.5), 5 units of the protein-deamidating enzyme wasadded to the suspension and the mixture was allowed to undergo theenzyme reaction at 37° C. for 20 hours on a shaker. The releasingpattern of ammonia during this reaction is shown in FIG. 10. It can beunderstood from the drawing that the deamidation reaction was generatedin the enzyme-added reaction system since ammonia was released with thepassage of the reaction time, which is contrary to the reaction carriedout in the absence of the enzyme as a control. After the reaction, thiswas dialyzed against distilled water and then freeze-dried to obtaindeamidated gluten powder.

The resulting deamidated gluten had a deamidation percentage of 37.4%.The deamidation percentage was determined by measuring the amount ofammonia released in the solution after the reaction and showed as apercentage to the total amido content of wheat gluten. The total amidocontent of protein was determined by hydrolyzing the protein (1% w/v) in2N hydrochloric acid at 100° C. for 2 hours and measuring ammoniarelease.

EXAMPLE 12

Improvement of Functionality (Solubility and Dispersibility) ofDeamidated Gluten

A 2.0 mg portion of each of the deamidated gluten powder obtained inExample 11 and enzyme-untreated gluten powder obtained by the controltest was suspended and dissolved in 1.0 ml of 40 mM Britton-Robinsonbuffer having a pH value of from 3 to 12, shaken at room temperature for30 minutes and then allowed to stand at room temperature for 30 minutes.After checking the pH value, this was centrifuged at a low speed of3,000 rpm (760×g) for 10 minutes at 24° C., and the protein content inthe thus obtained supernatant was measured by the BCA method. Theprotein content in the supernatant was used as an index of thedispersibility (Methods of Testing Protein Functionality, p. 25, editedby G. M. Hall, Blackie Academic & Professional, London, 1996).

The supernatant was further centrifuged at a high speed of 14,000 rpm(16,000 ×g) for 30 minutes at 24° C., the thus obtained supernatant wasfiltered through a 0.45 μm membrane and then the protein content in theresulting filtrate was measured by the BCA method. The protein contentin the filtrate was used as an index of the solubility (Methods ofTesting Protein Functionality, pp. 47-55, edited by G. M. Hall, BlackieAcademic & Professional, London, 1996).

As is evident from the results shown in FIGS. 11 and 12, when comparedwith the enzyme-untreated gluten, the deamidated gluten has markedlyimproved dispersibility and solubility within a broad pH range of fromaround pH 4.2 to around pH 12.

EXAMPLE 13

Production of Coffee Whitener Using Deamidated Gluten

A 5 g portion of deamidated gluten produced in accordance with themethod of Example 11 was mixed with 2 g of corn syrup, 0.4 g ofpolysorbate 60 and 51 g of water, and the mixture was heated at 40° C.and then mixed with 0.3 g of dipotassium hydrogenphosphate and heated to80° C. A 6 g portion of partially hydrogenated coconut oil and 0.2 g ofmonoglyceride were added under melted state to the mixture solution, andthe resulting mixture was hallowed to stand at 80° C. for 20 minutes,homogenized under a pressure of 211 kg/cm² and then cooled, therebyproducing a coffee whitener containing deamidated gluten. This productshowed a stable emulsion state, and showed excellent dispersibility,solubility and palatability when added to coffee.

EXAMPLE 14

Production of Tempura Flour

A 100 g portion of wheat flour was suspended in 1 liter of water, andthe suspension was mixed with 10 units of the protein-deamidatingenzyme, subjected to the enzyme reaction at 37° C. for 20 hours withshaking, dehydrated by centrifugation and then heat-dried to obtaindeamidation-treated wheat flour. A 50 g portion of the thus obtainedwheat flour was dissolved in 60 ml of water and used as a coatingsolution for tempura use. A prawn (Penaeus orientalis) (about 25 g) wasfloured, coated with the coating solution and then fried in arapeseed/soybean mixture oil at 170 to 180° C. for 3 minutes. The prawnwas also fried in the same manner using wheat flour which has not beentreated with the protein-deamidating enzyme. The wheat flour treatedwith the protein-deamidating enzyme showed excellent dispersibility whenthe coating solution was prepared, and the thus obtained fry wasmarkedly excellent in terms of eating touches such as hardness andcrispness of the coating, as well as its appearance and taste.

EXAMPLE 15

Production of Premix

A premix for hot cake use having the following composition was preparedusing the protein-deamidating enzyme-treated wheat flour which has beenprepared in accordance with the method of Example 14.

Protein-deamidating enzyme-treated wheat flour 72.0% Sugar 20.0%Expanding agent (sodium bicarbonate)  1.5% Oil and fat  3.0% Table salt 1.0% Gluconodeltalactone  2.0% Spice  0.5%

A 200 g portion of the thus prepared premix was put into a bowl to whichwere further added 150 ml of milk and 50 g of whole egg, and thecontents were mixed by whipping to obtain a dough for hot cake use. Acontrol dough was prepared in the same manner using untreated wheatflour. A 100 g portion of the thus obtained dough was spread in acircular form on a hot plate of 160° C., and its front side was bakedfor 4 minutes, and the back side for 2 minutes, thereby obtaining a hotcake.

Handling of the dough and softness, melting touch in the mouth andwetness of the hot cake were judged by a panel. As the results, all ofthese factors were superior to those of the control when theprotein-deamidating enzyme-treated wheat flour was used.

EXAMPLE 16

Preparation of Bread Dough

A one loaf bread was produced by a no time method using the followingformulation.

[Formulation]

Wheat flour 100% 2,000 g Sugar  15% 100 g Table salt  2% 40 g Shortening 4% 80 g Yeast  3% 60 g Ascorbic acid 20 ppm 40 mg Water  69% 1,380 ml

Using the above formulation as the base, a protein-deamidatingenzyme-added (7.5 units/1 kg wheat flour) group and an enzyme-free(control) group were prepared and compared.

[Steps]

-   (1) Mixing: 4 minutes at low speed→    -   4 minutes at high speed→    -   addition of shortening→    -   1 minute at low speed→    -   4 minute at medium speed→    -   4 minutes at high speed-   (2) Kneading Temperature: 27-29° C.-   (3) Floor Time: 27° C., 30 minutes-   (4) Separation: dough weight, 450 g-   (5) Bench Time: 30 minutes-   (6) Drying: 38° C., 3.5 cm on a bread case mold-   (7) Baking: 230° C., 25 minutes

In the protein-deamidating enzyme-added group, handling of the dough wasexcellent, and extensibility of the dough and softness of the bakedbread were improved.

EXAMPLE 17

Preparation of Biscuit Dough

A biscuit dough of the following composition was prepared usingprotein-deamidating enzyme-treated wheat flour which has been preparedin accordance with the method of Example 14.

Protein-deamidating enzyme-treated wheat flour  100 g Shortening   16 gSugar   50 g Sodium bicarbonate 0.81 g Potassium bitartarate  0.5 gWater   16 g Egg   2 g

Mixing, molding and baking (180-220° C.) were carried out in the usualway to prepare hard biscuits. Handling of the dough and improvement ofextensibility were significant, and eating touch of the preparedbiscuits was also excellent.

EXAMPLE 18

Preparation of Deamidated casein

A 1 g portion of milk casein was suspended in 100 ml of 176 mM sodiumphosphate buffer (pH 6.5), 5 units of the protein-deamidating enzyme wasadded to the suspension and the mixture was allowed to undergo theenzyme reaction at 37° C. for 20 hours on a shaker. The releasingpattern of ammonia during this reaction is shown in FIG. 13. It can beunderstood from the drawing that the deamidation reaction was generatedin the enzyme-added reaction system since ammonia was released with thepassage of the reaction time, which is contrary to the reaction carriedout in the absence of the enzyme as a control. After the reaction, thiswas dialyzed against distilled water and then freeze-dried to obtaindeamidated casein powder.

The resulting deamidated casein had a deamidation percentage of 40.9%.The deamidation percentage was determined by measuring the amount ofammonia released in the solution after the reaction and showed as apercentage to the total amido content of casein. The total amido contentof protein was determined by hydrolyzing the protein (1% w/v) in 2Nhydrochloric acid at 100° C. for 2 hours and measuring ammonia release.

The deamidated casein as well as an enzyme-untreated casein weresubjected to 10-20% SDS-PAGE. The resulting pattern is shown in FIG. 14.It is clear that the molecular weight of the deamidated casein (lane 2)did not change, i.e., degradation or cross-linking was not occurred.Although a slight shift of deamidated casein band to higher molecularweight side is observed, it is considered that this shift was due to theincrease in minus charges in protein by deamidation. In the presence ofSDS, total minus charges of deamidated casein should be low compared tothose of non-deamidated casein because the amount of SDS, which also hasminus charges, binding to deamidated casein should be less than that tonon-deamidated casein by electrostatic repulsion. The lower total minuscharges of deamidated casein should cause reduced migration in theelectophoresis.

EXAMPLE 19

Improvement of Calcium-Dependent Solubility of Deamidated Casein

A 2.0 mg portion of each of the deamidated casein powder obtained inExample 18 and enzyme-untreated casein powder obtained by the controltest was suspended and dissolved in 10 mM Tris-HCl buffer (pH 7.1)containing calcium chloride in an amount of from 0 to 30 mM, shaken atroom temperature for 30 minutes and then allowed to stand at roomtemperature for 30 minutes. This solution was centrifuged at a low speedof 3,000 rpm (760×g) for 10 minutes at 24° C., the resulting supernatantwas further centrifuged at a high speed of 14,000 rpm (16,000×g) for 30minutes at 24° C., the thus obtained supernatant was filtered through a0.45 μm membrane and then the protein content in the resulting filtratewas measured by the BCA method. The protein content in the filtrate wasused as an index of the calcium-dependent solubility.

As is evident from the results shown in FIG. 15, when compared with theenzyme-untreated casein, the deamidated casein shows high solubilityeven in the presence of high concentration of calcium, so that itscalcium-dependent solubility is markedly improved.

EXAMPLE 20

Production of Enzyme-Digested Liquid Seasoning

A 150 ml portion of 15% brine was added to 45 g of gluten to which werefurther added 50 units of the protein-deamidating enzyme, 0.1% ofGlutaminase F100 (manufactured by Amano Pharmaceutical Co., Ltd.) and0.75% of Protease M (manufactured by Amano Pharmaceutical Co., Ltd.),and the resulting mixture was allowed to undergo 3 to 4 days of thereaction at 45° C. After the reaction, the reaction mixture was heatedat 90° C. for 20 minutes to prepare an enzyme-digested liquid seasoning.It was able to produce an excellent liquid seasoning in which theformation of bitter components was reduced due to the improvement ofboth decomposition ratio and decomposition rate, in comparison with acontrol liquid seasoning prepared in the same manner without adding theprotein-deamidating enzyme.

EXAMPLE 21

Method for the Concentration and Recovery of Soybean Protein andProduction of Deamidated Soybean Protein

A 100 g portion of soybean flour was suspended and dissolved in 1 literof water which was subsequently adjusted to pH 6.5 while stirring, mixedwith 500 units of the protein-deamidating enzyme and then stirred atroom temperature for 2 hours. After the reaction, this was adjusted topH 8, stirred for 1 hour and then centrifuged at 10,000 rpm (12,300×g)for 30 minutes at room temperature to remove insoluble matter. In orderto recover protein from the thus obtained supernatant, the supernatantwas subjected to 30 minutes of heat treatment at 80° C. and then to 30minutes of centrifugation at 10,000 rpm (12,300×g), and then the thusformed precipitate was recovered and dried to obtain protein powder. Theprotein content of this protein powder was 95%, and it was obtained witha high yield of about 40% from soybean flour.

EXAMPLE 22

Production of Sausage Using Deamidated Soybean Protein

The deamidated soybean protein produced in accordance with the method ofExample 21 was subjected to a coagulation treatment by repeating itsstirring, extrusion and rolling steps. The thus coagulated soybeanprotein was kneaded with meat materials and various spices according tothe following formulation and then packed in casings in the usual way toproduce sausages. The thus obtained product was markedly excellent interms of palatability.

Pork shoulder  500 g Beef round  500 g Pork ground fat  100 g Coagulatedsoybean protein  100 g Table salt   25 g Potassium nitrate   3 g Sugar  5 g Ajinomoto (sodium glutamate)   3 g White pepper   3 g Nutmeg   4 gCinnamon  0.5 g Onion juice   5 g

EXAMPLE 23

Use as a Transglutaminase Reaction Controlling Agent

A 12.5 μl portion of a solution containing 0.0125 unit ofStreptoverticillium transglutaminase (prepared in accordance with themethod described in Agric. Biol. Chem., vol. 53, no. 10, pp. 2613-2617,1989) was added to 25 μl of 20 mM phosphate buffer (pH 7.0) containing10% casein, and the resulting solution was stirred and then allowed tostand at 37° C. to effect the enzyme reaction. One hour thereafter, 12.5μl of a solution containing 0.0188 unit of the protein-deamidatingenzyme was added thereto, and the mixture was stirred and then allowedto stand at 37° C. A portion of the reaction solution was sampled after1, 2, 4 or 24 hours of the reaction and subjected to SDS-polyacrylamidegel electrophoresis using 2 to 15% SDS-polyacrylamide gel. As a control,the same test was carried out using a sample obtained by adding waterinstead of the protein-deamidating enzyme solution.

The results are shown in FIG. 16, and the samples applied to respectivelanes in FIG. 16 are shown in Table 5.

TABLE 5 Lane Protein-deamidating enzyme Time (h) 1 − 0 2 − 1 3 − 2 4 − 45 − 24 6 − 0 7 + 1 8 + 2 9 + 4 10 + 24

As in evident from the results shown in FIG. 16, in the control reactionin which the protein-deamidating enzyme was not added, molecular weightof the protein increases with the lapse of time by its cross-linkingreaction and the band of casein monomer observed at 0 hour decreases anddisappears, while the pattern at the time of the addition of theprotein-deamidating enzyme (lane 7) does not change with the lapse oftime in the reaction in which the enzyme was added. This means that thecross-link polymerization reaction of transglutaminase was stopped bythe addition of the protein-deamidating enzyme.

A solution (12.5 μl) containing 0.0125 units of transglutaminase derivedfrom Streptoverticillium was added to 25 μl of 20 mM phosphate buffer(pH 7.0) containing 10% deamidated casein obtained in Example 18, themixture was stirred and then allowed to stand at 37° C. A portion of thereaction solution was sampled after 1, 2, 4 to 24 hours of the reactionand subjected to SDS-polyacrylamide gel electrophoresis using 2 to 15%SDS-polyacrylamide gel. As a control, the same test was using untreatedcasein instead of deamidated casein.

The results are shown in FIG. 17, and the samples applied to respectivelanes in FIG. 17 are shown in Table 6.

TABLE 6 Lane Substrate protein Time (h) 1 Deamidated casein 0 2Deamidated casein 1 3 Deamidated casein 2 4 Deamidated casein 4 5Deamidated casein 24 6 casein 0 7 casein 1 8 casein 2 9 casein 4 10casein 24

As is evident from the results shown in FIG. 17, in the control reactionin which the enzyme-untreated casein was used, molecular weight of theprotein increases with the lapse of time by its cross-linking reactionand the band of casein monomer observed at 0 hour decreases anddisappears, while the band observed at 0 hour in the reaction usingdeamidated casein (lane 1) does not change with the lapse of time in thereaction. This means that proteins deamidated by the protein-deamidatingenzyme cannot be a substrate for the transglutaminase.

EXAMPLE 24

Production of Pudding-Like Food Using Transglutaminase andProtein-Deamidating Enzyme

Commercially available milk was concentrated under a reduced pressure, 5g of sugar was dissolved in the thus obtained concentrate and then theresulting solution was mixed with 1 unit of Streptoverticilliumtransglutaminase and incubated at 55° C. When appropriate gel wasformed, the gel was mixed with 1.5 units of the protein-deamidatingenzyme and stirred to stop the transglutaminase reaction and thencooled. As the results, it was able to produce a pudding-like foodpreparation having desirable softness.

EXAMPLE 25

Improvements in Functionality of Deamidated Casein (Solubility andDispersibility)

Deamidated casein powder obtained in Example 18 and enzyme-untreatedcasein obtained in comparative experiment were measured for thesolubility and dispersibility by the method similar to Example 12.

As shown in FIG. 18, deamidated casein showed extremely improveddispersibility and solubility in comparison with enzyme-untreatedcasein, expecially at the pH range of usual foods (i.e., from about pH 4to about pH 5).

The following examples are provided to further illustrate the presentinvention. Unless otherwise noted, the gene manipulation techniques werecarried out in accordance with the methods described in the literatures(for example, “Molecular Cloning” 2nd ed., Cold Spring Harbor LaboratoryPress, 1989).

EXAMPLE 26

Isolation of Gene Coding for Chryseobacterium gleum JCM 2410Protein-Deamidating Enzyme

a) Isolation of Chromosomal DNA

A 3.3 ml of chromosomal DNA solution having a concentration of 190 μg/mlwas obtained from 100 ml of culture in accordance with the methoddescribed in “Current Protocols in Molecular Biology”, Unit 2.4 (JohnWiley & Sons, Inc., 1994).

b) Determination of Partial Amino Acid Sequence

The purified protein-deamidating enzyme obtained in Example 9 wasapplied to a protein sequenser (manufactured by Applied Biosystems) todetermine an N-terminal amino acid sequence of 20 residues shown in theSequence No. 1. Next, the purified protein-deamidating enzyme obtainedin Example 9 was reduced and alkylated using performic acid and thenhydrolyzed with trypsin. The thus obtained hydrolysate was applied to areverse phase liquid chromatography, and one of the separated peptidefractions was applied to the protein sequenser to determine an internalamino acid sequence of 20 residues shown in the Sequence No. 2.

Sequence No. 1: Ala-Val-Ser-Val-Ile-Pro-Asp-Leu-Ala-Thr-Leu-Asn-Ser-Leu-Phe-Thr-Gln-Ile-Lys-Asn Sequence No. 2:Ser-Pro-Ser-Gly-Ser-Leu-Leu-Tyr-Asp-Asn-Asn-Tyr-Val-Asn-Thr-Asn-Cys-Val-Leu-Asnc) Preparation of DNA Probe by PCR

Based on the N-terminal region amino acid sequence and the internalamino acid sequence, the following two mixed oligonucleotides weresynthesized using a DNA synthesizer (manufactured by Applied Biosystems)and used as PCR primers.

Sequence No. 3 Sense primer: 5′-(TA) (CG) IGTIAT (TCA) CCIGA (TC) (CT) T(TCAG) AC-3′ Sequence No. 4 Antisense primer: 5′-A (AG) (TCAG) AC (AG)CA (AG) TT (TCAG) GT (AG) TT (TCAG) AC-3′

Using these primers and the Chryseobacterium gleum JCM 2410 chromosomalDNA as the template, PCR reaction was carried out using Omnigene ThermalCycler (manufactured by Hybaid) under the following conditions.

<PCR Reaction Solution>

10 × PCR reaction buffer (manufactured by Perkin 5.0 μl Elmer) dNTPmixture solution (each 2.5 mM, manufactured by 4.0 μl Promega) 20 μMsense primer 10.0 μl 20 μM antisense primer 10.0 μl distilled water20.25 μl chromosomal DNA solution (190 μg/ml) 0.5 μl Taq DNA polymerase(manufactured by Perkin Elmer) 0.25 μl

<PCR Reaction Condition>

Stage 1: denaturation (94° C., 5 minutes) 1 cycle Stage 2: denaturation(94° C., 1 minute) 30 cycles annealing (44° C., 1 minute) elongation(72° C., 1 minute) Stage 3: elongation (72° C., 10 minutes) 1 cycle

When the thus obtained DNA fragment of about 0.48 kb was cloned intopCRII (manufactured by Invitrogene) and then its nucleotide sequence wasdetermined, a nucleotide sequence coding for the aforementioned partialamino acid sequence was found in a region just after the sense primerand just before the antisense primer. This DNA fragment was used as aDNA probe for use in the cloning of the complete gene.

d) Preparation of Gene Library

As a result of the Southern hybridization analysis of theChryseobacterium gleum JCM 2410 chromosomal DNA, a single band of about3.7 kb capable of hybridizing with the probe DNA was found in an EcoRIdigest. In order to carry out cloning of this EcoRI DNA fragment ofabout 3.7 kb, a gene library was prepared in the following manner. Thechromosomal DNA prepared in the aforementioned step a) was digested withEcoRI, and the thus obtained digest was ligated to an EcoRI-treated λZAPII (manufactured by Stratagene) and packaged using Gigapack III Gold(manufactured by Stratagene) to obtain the gene library.

e) Screening of Gene Library

The 0.48 kb DNA fragment obtained in the aforementioned step c) waslabeled using Megaprime DNA Labeling System (manufactured by Amersham)and ³²P-α-dCTP. Using this as a DNA probe, the gene library obtained inthe above step d) was screened by plaque hybridization. Phage particleswere recovered from the thus obtained positive plaques, and then aplasmid p7T-1 containing an EcoRI fragment of about 3.7 kb was obtainedby the in vivo excision method in accordance with the instructionprovided by Stratagene.

f) Determination of Nucleotide Sequence

Nucleotide sequence of the plasmid p7T-1 was determined in theconventional way. The nucleotide sequence which encodes theprotein-deamidating enzyme is shown in Sequence No. 5. Also, amino acidsequence encoded by the Sequence No. 5 is shown in Sequence No. 6. TheN-terminal region amino acid sequence (Sequence No. 1) and internalamino acid sequence (Sequence No. 2) determined in the aforementionedstep b) were found in this amino acid sequence.

Sequence No. 5 GCAGTCAGTGTTATTCCTGATCTGGCAACGCTGAACAGTTTATTTACCCAGATCAAAAACCAGGCTTGCGGAACTTCTACAGCATCTTCTCCTTGTATCACCTTCAGATATCCGGTTGACGGATGTTATGCAAGGGCTCACAAAATGAGACAAATCCTATTGAACGCCGGCTATGACTGTGAAAAGCAGTTCGTATATGGTAATCTGAGAGCTTCTACAGGAACATGCTGTGTATCATGGGTATATCACGTAGCAATTTTGGTAAGCTTCAAAAATGCTTCAGGAATTGTTGAAAAAAGAATCATAGATCCTTCATTATTCTCCAGCGGTCCTGTAACAGATTCTGCATGGAGAGCTGCATGTACCAACACAAGCTGCGGATCTGCGTCTGTATCTTCCTACGCCAATACAGCAGGAAATGTTTACTACAGAAGTCCGTCAGGTTCATTACTGTATGATAACAACTATGTGAATACCAATTGTGTATTAAACATATTCTCATCCCTTTCAGGATGTTCTCCTTCCCCAGCACCAAGTGTAGCAAGCTGTG GATTT (555 bp)Sequence No. 6 AVSVIPDLATLNSLFTQIKN QACGTSTASSPCITFRYPVDGCYARAHKMRQILLNAGYDC EKQFVYGNLRASTGTCCVSW VYHVAILVSFKNASGIVEKRIIDPSLFSSGPVTDSAWRAA CTNTSCGSASVSSYANTAGN VYYRSPSGSLLYDNNYVNTNCVLNIFSSLSGCSPSPAPSV ASCGF (185 amino acids)

The open leading frame of this gene is shown in Sequence No. 11 below. Aprepro protein having 319 amino acid residues as shown in Sequence No.12 below are encoded by the gene, in which N-terminal 134 amino acidresidues (underlined in Sequence No. 11) correspond to the prepro regionand the remaining 185 amino acid residues correspond to the matureprotein (cf. Sequence No. 6). Among the 134 residues of the preproregion, the N-terminal 21 residues have the characteristics of thesignal sequence. Accordingly, it is considered that the N-terminal 21residues correspond to the pre region and remaining 113 residuescorrespond to the pro region.

The present invention is not particularly limited to polypeptides havingprotein-deamidating activity and nucleotides encoding the same, but alsoincludes the longer polypeptides comprising the polypeptides havingprotein-deamidating activity (e.g., prepro proteins, pro proteins, andthe like) and nucleotides encoding the same.

Sequence No. 11AATAAGTGAACTATTACAATTAAAAAGTTCACTAAAACTAAACACCAAAATATAAAAACTATGAAAAAATTTCTGTTATCCATGATGGCATTCGTGACGATTCTGTCATTCAATGCCTGC 1M K K F L L S M M A F V T I L S F N A C 20TCAGATTCAAGTGCCAACCAGGACCCGAATCTTGTCGCTAAAGAATCTAACGAAGTCGCT 21S D S S A N Q D P N L V A K E S N E V A 40ATGAAAGATTTCGGTAAGACTGTTCCGGTAGGGATTGAAAAAGAAGATGGAAAATTTAAA 41M K D F G K T V P V G I E K E D G K F K 60ATCTCATTTATGGTTACTGCCCAGCCGTATGAAATTGCGGACAGTAAAGAAAATGCAGGT 61I S F M V T Q P Y E I A D S K E N A G 80TATATTTCCATGATCAGACAGGCTGTTGAGAATGAAACTCCCGTTCATGTTTTCCTTAAA 81Y I S M I R Q A V E N E T P V H V F L K 100GTCAACACCAATAAAATTGCAAAAGTAGAAAAAGCAACAGATGATGACATCCGTTATTTT 101V N T N K I A K V E K A T D D D I R Y F 120AAATCTGTATTCAACAAGCAAGAGAGAGGTGAAAGCAACAAAGCAGTCAGTGTTATTCCT 121K S V F N K Q E R G E S N K A V S V I P 140GATCTGGCAACGCTGAACAGTTTATTTACCCAGATCAAAAACCAGGCTTGCGGAACTTCT 141 D L A TL N S L F T Q I K N Q A C G T S 160ACAGCATCTTCTCCTTGTATCACCTTCAGATATCCGGTTGACGGATGTTATGCAAGGGCT 161 T A S SP C I T F R Y P V D G C Y A R A 180CACAAAATGAGACAAATCCTATTGAACGCCGGCTATGACTGTGAAAAGCAGTTCGTATAT 181 H K M RQ I L L N A G Y D C E K Q F V Y 200GGTAATCTGAGAGCTTCTACAGGAACATGCTGTGTATCATGGGTATATCACGTAGCAATT 201 G N L RA S T G T C C V S W V Y H V A I 220TTGGTAAGCTTCAAAAATGCTTCAGGAATTGTTGAAAAAAGAATCATAGATCCTTCATTA 221 L V S FK N A S G I V E K R I I D P S L 240TTCTCCAGCGGTCCTGTAACAGATTCTGCATGGAGAGCTGCATGTACCAACACAAGCTGC 241 F S S GP V T D S A W R A A C T N T S C 260GGATCTGCGTCTGTATCTTCCTACGCCAATACAGCAGGAAATGTTTACTACAGAAGTCCG 261 G S A SV S S Y A N T A G N V Y Y R S P 280TCAGGTTCATTACTGTATGATAACAACTATGTGAATACCAATTGTGTATTAAACATATTC 281 S G S LL Y D N N Y V N T N C V L N I F 300TCATCCCTTTCAGGATGTTCTCCTTCCCCAGCACCAAGTGTAGCAAGCTGTGGATTTTAA 301 S S L SG C S P S P A P S V A S C G F * 319TTTTGATACATTGCAGGAGCTTTTTATTTAATACTTTTTATTATGAAAGCCTGGTCCTAT (1080)Sequence No. 12 M K K F L L S M M A F V T I L S F N A C S D S S A N Q DP N L V A K E S N E V A M K D F G K T V P V G I E K E D G K F K I S F MV T A Q P Y E I A D S K E N A G Y I S M I R Q A V E N E T P V H V F L KV N T N K I A K V E K A T D D D I R Y F K S V F N K Q E R G E S N K A VS V I P D L A T L N S L F T Q I K N Q A C G T S T A S S P C I T F R Y PV D G C Y A R A H K M R Q I L L N A G Y D C E K Q F V Y G N L R A S T GT C C V S W V Y H V A I L V S F K N A S G I V E K R I I D P S L F S S GP V T D S A W R A A C T N T S C G S A S V S S Y A N T A G N V Y Y R S PS G S L L Y D N N Y V N T N C V L N I F S S L S G C S P S P A P S V A SC G F

EXAMPLE 27

Production of Protein-Deamidating Enzyme in Escherichia coli

a) Construction of Plasmid for Use in the Expression ofProtein-Deamidating Enzyme in Escherichia coli

Based on the DNA sequences which encode the N-terminal region amino acidsequence and the C-terminal region amino acid sequence, the followingtwo oligonucleotides were synthesized using a DNA synthesizer(manufactured by Applied Biosystems) and used as PCR primers.

Sequence No. 7 Sense primer: 5′-GCGAATTCGCAGTCAGTGTTATTCCTGATC-3′Sequence No. 8 Antisense primer: 5′-TAGAATTCTTAAAATCCACAGCTTGCTAC-3′

Using these primers and the protein-deamidating enzyme gene-containingplasmid p7T-1 as the template, PCR reaction was carried out usingOmnigene Thermal Cycler (manufactured by Hybaid) under the followingconditions.

<PCR Reaction Solution>

10 × PCR reaction buffer (manufactured by Perkin Elmer) 10.0 μl dNTPmixture solution (each 2.5 mN, manufactured by 8.0 μl Promega) 20 μMsense primer 2.5 μl 20 μM antisense primer 2.5 μl distilled water 75.5μl plasmid p7T-1 solution (50 μg/ml) 1.0 μl Taq DNA polymerase(manufactured by Perkin Elmer) 0.5 μl

<PCR Reaction Condition>

Stage 1: denaturation (94° C., 5 minutes) 1 cycle Stage 2: denaturation(94° C., 1 minute) 30 cycles annealing (55° C., 1 minute) elongation(72° C., 1 minute) Stage 3: elongation (72° C., 10 minutes) 1 cycle

The thus obtained DNA fragment of about 0.57 kb was cloned into pCRII(manufactured by Invitrogene) to confirm that the nucleotide sequencewas correct, and then the DNA fragment of about 0.57 kb was recoveredfrom the plasmid by EcoRI treatment. This DNA fragment was inserted intoan expression vector pGEX-1λT for E. coli use (manufactured byPharmacia), and the protein-deamidating enzyme-encoding DNA wasconnected to the C-terminal-corresponding side of the glutathione Stransferase-encoding DNA contained in the pGEX-1λT, in the samedirection. The thus obtained plasmid pN7-7 for use in the expression ofprotein-deamidating enzyme in E. coli can express a fusion protein ofglutathione S transferase with protein-deamidating enzyme under controlof tac promoter, and the protein-deamidating enzyme can be cut off fromthe fusion protein by thrombin treatment.

b) Expression of Protein-Deamidating Enzyme in E. coli

A transformant was obtained by introducing the expression plasmid pN7-7into E. coli BL21 (manufactured by Pharmacia). As a control, atransformant of E. coli BL21 having the expression vector pGEX-1λT wasalso obtained. Each of these transformants was cultured at 37° C. on a200 rpm rotary shaker using LB medium containing 100 μg/ml ofampicillin, and the cells obtained at the logarithmic growth phase(OD₆₀₀=0.9-1.0) were mixed with 0.1 mM in final concentration of IPTG,cultured for 4 hours under the same conditions and then collected. Thethus collected cells were suspended in 1/10 volume culture broth of 50mM Tris-HCl (pH 8.0)/2 mM MEDTAL mixed with 0.1 mg/ml in finalconcentration of egg white lysozyme and 0.1% in final concentration ofTriton X-100 and allowed to stand at 30° C. for 15 minutes, and then thethus formed viscous DNA was sheared by mild ultrasonic treatment (3cycles of 10 sec. on and 30 sec. off) to obtain a cell extract. A 100 μlportion of the cell extract was mixed with 4 μl of thrombin (1 U/μl in 9mM sodium phosphate (pH 6.5)/140 mM NaCl) and allowed to stand at roomtemperature for 16 hours to obtain thrombin-treated cell extract. Asample obtained by adding 4 μl of a buffer solution (9 mM sodiumphosphate (pH 6.5)/140 mM NaCl) and carrying out the same reaction wasused as a control of the thrombin treatment.

The protein-deamidating enzyme activity of the thus obtained sampleswere measured, with the results shown in the following table.

TABLE 7 Protein deamidation activity (mU/ml) Thrombin Substrate:Substrate: Sample Transformant treatment Z-Gln-Gly casein 1 E. coliBL21/pN7-7 − 30.02 16.10 2 E. coli BL21/pN7-7 + 35.36 19.99 3 E. coliBL21/pGEX-1λT − 0.00 0.00 4 E. coli BL21/pGEX-1λT + 0.00 0.00

Thus, it is apparent that the E. coli strain having theprotein-deamidating enzyme expression plasmid pN7-7 expresses theprotein deamidation activity. On the contrary, expression of the proteindeamidation activity was not found in the control E. coli strain havingthe expression vector pGEX-1λT. Separately from this, each of thesesamples was subjected to 12% SDS-polyacrylamide gel electrophoresis tocarry out Western blotting analysis using an antibody specific for theprotein-deamidating enzyme. As a result, a band which reacted with theantibody was detected in the sample 1 at a position of about 43 kDa inmolecular weight which seemed to be a fusion protein of glutathione Stransferase with the protein-deamidating enzyme, and a band was detectedin the sample 2 at a position of about 20 kDa in molecular weightcorresponding to the protein-deamidating enzyme, in addition to the bandof about 43 kDa in molecular weight. On the other hand, a band capableof reacting with the antibody was not detected in the samples 3 and 4.On the basis of these results, it was confirmed that a recombinantprotein-deamidating enzyme can be produced in E. coil using theprotein-deamidating enzyme gene obtained by the present invention.

EXAMPLE 28

Expression of Protein-Deamidating Enzyme in Filamentous Fungi

a) Construction of Expression Cassette for Protein-Deamidating Enzyme inFilamentous Fungi

Based on the DNA sequences which encode the N-terminal region amino acidsequence and the C-terminal region amino acid sequence, the followingtwo oligonucleotides were synthesized using a DNA synthesizer(manufactured by Applied Biosystems) and used as PCR primers.

Sequence No. 9 Sense primer: 5′-GCGTCGACGCAGTCAGTGTTATTCCTGATC-3′Sequence No. 10 Antisense primer: 5′-TAGGATCCTTAAAATCCACAGCTTGCTAC-3′

Using these primers and the protein-deamidating enzyme gene-containingplasmid p7T-1 as the template, PCR reaction was carried out in the samemanner as described in Example 27. The thus obtained DNA fragment ofabout 0.57 kb was cloned into pCRII (manufactured by Invitrogene) toconfirm that the nucleotide sequence was correct, and then the DNAfragment of about 0.57 kb was recovered from the plasmid by SalI/BamHItreatment. This DNA fragment was inserted into the SalI/BamHI site of afilamentous fungi expression cassette construction vector pY4′(JP-A-123987) to obtain a plasmid pD5′. This plasmid contains a DNAsequence which encodes a fusion protein composed of mono anddiacylglycerol lipases originated from Penicillium camembertii and theprotein-deamidating enzyme. An unnecessary nucleotide sequence existingin the connecting part of the mono and diacylglycerol lipases andprotein-deamidating enzyme (5′-GTCGAC-3′, this sequence corresponds tothe SalI site introduced to connect the protein-deamidating enzyme gene)of this plasmid was deleted by site-specific mutation to obtain aplasmid pD5. This plasmid contains a DNA sequence which encodes a fusionprotein in which the protein-deamidating enzyme is connected to justafter the processing sites of C-terminal regions of the mono anddiacylglycerol lipases (Lys-Arg sequences, 3rd and 2nd positions fromthe C-terminal, respectively). This fusion protein is expressed infilamentous fungi and yeast under control of the promoter and terminatorof the Penicillium camembertii mono and diacylglycerol lipase genes,which are present in its upstream and downstream regions. Also, theprotein-deamidating enzyme can be cut off from the thus expressed fusionprotein through its digestion at the Lys-Arg site by a protease of thehost (JP-A-7-123987).

b) Expression of Protein-Deamidating Enzyme in Penicillium camembertii

The plasmid pD5 obtained in the above step a) was introduced intoPenicillium camembertii U-150 by co-transformation together with aPenicillium camembertli transformation plasmid pH1. As a control, atransformant was obtained using pH1 alone. When the thus obtainedtransformants were cultured and the protein-deamidating enzyme activityin the culture filtrates was measured, production of 10.3 mU/ml(substrate, Z-Gln-Gly) of the protein-deamidating enzyme was found inthe transformant transformed with the plasmid pD5. On the other hand,the activity was not detected in the culture filtrate of thetransformant transformed with plasmid pH1 alone. In this connection, theplasmid pH1 and its transformation method are described in detail inJP-A-7-123987.

EXAMPLE 29

Expression of Protein-Deamidating Enzyme in Aspergillus oryzae

The plasmid pD5 obtained in the step a) of Example 28 was introducedinto Aspergillus oryzae AO1.1 (Mol. Gen. Genet., 218, 99-104, 1989) byco-transformation together with an Aspergillus oryzae transformationplasmid pN3. As a control, a transformant was obtained using pN3 alone.When the thus obtained transformants were cultured and theprotein-deamidating enzyme activity in the culture filtrates wasmeasured, production of 4.51 mU/ml (substrate, Z-Gln-Gly) of theprotein-deamidating enzyme was found in the transformant transformedwith the plasmid pD5. On the other hand, the activity was not detectedin the culture filtrate of the transformant transformed with plasmid pN3alone. In this connection, the plasmid pN3 and its transformation methodare described in detail in JP-A-7-123987.

It was confirmed based on the results of Examples 28 and 29 that arecombinant protein-deamidating enzyme can be produced by filamentousfungi utilizing the protein-deamidating enzyme gene obtained by thepresent invention.

A novel enzyme capable of acting upon glutamine in protein and therebycatalyzing the deamidation reaction was found for the first time inmicroorganisms, and a broad range of applications are expected by thisenzyme.

Also, since the primary structure and gene structure of theprotein-deamidating enzyme were provided by the present invention,inexpensive and high purity production of polypeptide havingprotein-deamidating enzyme activity by gene engineering techniquesbecame possible.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

This application is based on Japanese patent application No. Hei.10-173940, filed on Jun. 4, 1998, and incorporated herein by reference.

1. A method for modifying a target protein or peptide with a molecularweight of 5,000 or more, comprising allowing an enzyme, which is capableof deamidating amido groups in target proteins and peptides by directlyacting upon said amido groups, without cutting peptide bonds and withoutcross-linking said target proteins or peptides, to act on said targetprotein or peptide, wherein said enzyme is selected from the groupconsisting of (a) a polypeptide which comprises the amino acid sequenceset forth in SEQ ID NO:6, (b) a polypeptide which comprises the aminoacid sequence encoded by the nucleotide sequence set forth in SEQ IDNO:5, and (c) a polypeptide which comprises the amino acid sequenceencoded by the nucleotide sequence which has a homology of 80% or morewith the nucleotide sequence set forth in SEQ ID NO:5.
 2. The method ofclaim 1, wherein said target protein or peptide to be modified isderived from a plant or animal such that the solubility, dispersibility,foamability, foam stability, emulsification ability, and emulsificationstability of said protein or peptide is improved in comparison to thatof the protein or peptide untreated with said enzyme.
 3. The method ofclaim 1, wherein said target protein or peptide to be modified isderived from food such that the solubility, dispersibility, foamability,foam stability, emulsification ability, and emulsification stability ofsaid food is improved in comparison to that of the food untreated withsaid enzyme.
 4. The method of claim 1, wherein said target protein orpeptide is contained in a crude material such that the extractionefficiency of said target protein or peptide is improved in comparisonto that of the protein or peptide untreated with said enzyme.
 5. Amethod for controlling a transglutaminase reaction, which comprisesusing an enzyme having an activity to deamidate amido groups in targetprotein and peptide by directly acting upon the groups without causingsevering of peptide bond and cross-linking of protein, wherein saidenzyme is selected from the group consisting of (a) a polypeptide whichcomprises the ammo acid sequence set forth in SEQ ID NO:6, (b) apolypeptide which comprises the amino acid sequence encoded by thenucleotide sequence set forth in SEQ ID NO:5 and (c) a polypeptide whichcomprises the amino acid sequence encoded by the nucleotide sequencewhich has a homology of 80% or more with the nucleotide sequence setforth in SEQ ID NO:5 and said target protein or peptide has a molecularweight of 5,000 or more.
 6. The method of claim 5, wherein said enzymeis allowed to act on said target protein or peptide before saidtransglutaminase is allowed to act on said target protein or peptide. 7.The method of claim 5, wherein said transglutaminase is allowed to acton the target protein or peptide before said enzyme is allowed to act onsaid target protein or peptide.
 8. The method of claim 5, wherein saidenzyme and said transglutaminase are allowed to act on said targetprotein or peptide at the same time.
 9. The method of claim 1, whichfurther comprises the step of allowing a protease and a glutaminase toact on said target protein or peptide.